1. Field of the Invention
The present invention relates to a sequential hydraulic control device of a machine, that is, a device in which there is a hydraulic control pressure which is a direct function of the results it is wished to obtain from the machine.
2. Description of the Prior Art
Machine tools, presses, automobiles and numerous other types of machines can be actuated automatically by hydraulic control means consisting in the main of a hydraulic pressure generator and distributors directing the pressure delivered by the generator into jacks or motors. The distributors are generally controlled by electromagnets which consume a fairly high electric power of the order of several tens of watts and with a high inductance. These electromagnets are themselves controlled automatically by electric circuits comprising essentially contactors consisting in principal of a distributor contactor, contactors which open or close as a function of a parameter such as the time, the speed of the vehicle, etc. In devices of this type, the electric circuit is very expensive. It may represent more than a third of the price of the entire device, mainly due to the fact that contactors are needed with have a high cut-off capacity. Furthermore, control units of this type function either completely or not at all.